Wal-Mart is working with big-rig and heavy-duty commercial hybrid trucks makers like Peterbilt and ArvinMeritor to test the new technologies.

"In order to meet our goal of doubling our fleet efficiency, we are taking an active role in the development of these technologies," said Chris Sultemeier, senior vice president of transportation for Wal-Mart Stores. "We look forward to determining if these technologies will help reduce our environmental footprint, are viable for our business and provide a return on investment."

Wal-Mart,